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A SUMMARY OF STUDIES OF LOCO-WEED DISEASE 

OF SHEEP. 

By Harry T. Marshall, A. B., M. D./ Charlottesville, Va. 



[From The Johns Hopkins Hospital Bulletin, Vol. XXV, No. 282, 

August, 1914.] 



A SUMMARY OF STUDIES OF LOCO-WEED DISEASE 

OF SHEEP. 1 

By Harry T. Marshall, A. B., M. D., Charlottesville, Va. 

Eleven years ago, during the summer of 1903, 1 was engaged [234] 
by the United States Department of Agriculture to investi- 
gate loco-weed disease in Montana, and I continued this study 
during the summer of 1904. The data thus obtained were 
worked up into two reports to the Department of Agriculture 
submitted in 1904 and in the spring of 1906. A more com- 
plete technical report was also submitted to the Department. 
The reports have not been published by the Department, and 
recently Secretary Houston has given me permisson to publish 
elsewhere. The full details of my studies will soon be pub- ■ 
lished in the Bulletin of the Philosophical Society of the Uni- 
versity of Virginia, Vol. I. In this article I shall give a brief 
review of my detailed report. 

Widely spread over the western ranges from Canada to 
Mexico and from Kansas to California are many plants called 
loco-weeds. The plants properly called loco-weeds conform to 
two or three main types, all of which are members of the family 
Leguminosse. These plants are hardy; bloom luxuriantly in 
the early summer and maintain themselves even where the soil 
is very poor, being most abundant, probably, in the higher 
plains and foothills east of the Rockies though not limited to 
this locality. 

According to popular opinion, animals which feed upon 
these plants are attacked in the most remarkable way. They 
become crazy, hence the name " loco " or " crazy " disease ; 
they are affected by the most peculiar mental and nervous 
symptoms; they become drug fiends, in that they want little 
else than the loco-weed to eat; they sooner or later emaciate 
and die from exhaustion or intercurrent disease. The length 
of the disease is not clearly described and many of the symp- 

1 Published by permission of the Secretary of Agriculture. 

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[234] toms are extremely vague. Animals are supposed to teach 
one another the habit of eating loco-weed and often the disease 
will go through an entire herd or flock. The disease entered 
the United States from Mexico in the early stock-raising days 
of the wesl and gradually swept north and now it is found as 
far north as Montana. The losses resulting from it are sup- 
posed to be perfectly enormous, partly directly by death, but 
to a greater extent from the depreciation of the animals which 
are supposed rarely to recover. 

Experimental studies upon the loco-weed and feeding experi- 
ments have given the most contradictory results, but it is safe 
to say that no one has succeeded in definitely identifying any 
poisonous principle, inherent in the loco-weed, and capable of 
producing the symptoms popularly associated with loco disease. 

My studies were confined to the locoed sheep of Montana. 
Other locoed animals could not be obtained for study even 
after extended search for them. Most exhaustive inquiries 
were made of stock raisers concerning various aspects of the 
symptoms, the etiology and course of the disease. These in- 
quiries alone served to show that stock raisers had not a single 
clear cut disease in mind in describing loco disease; the de- 
scription of one stockman not tallying with that of another. 
It appeared probable from studying as a composite picture the 
information thus obtained that loco disease was something in 
the nature of an infectious process or at least that it was 
communicable, and that it attacked especially the younger and 
weaker animals and prevailed more particularly over ranges 
and feedings grounds which had been in use for ten or more 
years. 

An important part of my work ' consisted in inspecting 
flocks of sheep suffering from loco disease and in examining 
in detail the most typical cases of severe loco selected from 
these flocks. Detailed autopsies were performed upon the 
selected animals after the symptoms had been studied as care- 
fully as possible. The autopsy tissues were studied micro- 
scopically. It was hoped that these studies would establish 
postively the symptoms of loco-weed poisoning, and would 
reveal any anatomic changes resulting in animals which were 
victims of the locoweed. 

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It soon become evident that the " locoed " sheep from differ- [234] 
ent flocks were not affected by the same disease. One flock, 
for example, presented emaciation and weakness as the chief 
symptoms, and at antopsy these sheep were found to be heavily [235] 
infected with a tapework of the liver, " Thysanosoma actin- 
ioides." 2 ,A second group of sheep which were supposed to be 
typical locoes were overcome with bronchitis and respiratory 
distress. In these cases lung worms and pneumonias were very 
common. A third group of sheep whose behavior was regarded 
as most typical of locoed animals were found to be suffering 
from nasal and respiratory difficulties which were definitely 
proved to be associated with severe sheep fly infection (Oestrus 
ovis) . A few other forms of parasite were encountered but the 
above mentioned were the most significant. In addition to 
these infections it became clear from inspection and from care- 
ful inquiry of the stock raisers themselves that the sheep in 
Montana, generally speaking, were insufficiently nourished. 
The ranges are grazed over so frequently that the grass does 
not have a chance to attain a good growth in the intervals 
between grazings; the flocks are too large for the available 
grazing grounds, while the grazing grounds are becoming cur- 
tailed as more and more open range is fenced in. Moreover 
in a large flock the delicate sheep have little chance to obtain 
good nourishment as they are crowded into the background by 
the stronger sheep. 

A most careful study of the sheep failed to reveal anything 
in the least distinctive of the hypothetical loco poisoning either 
clinically or. anatomically. The locoed sheep presented not a 
uniform picture as of a single disease, but varied appearances 
as from different diseases, any of which may be called loco 
disease by the ranchmen. The abnormalities observed in the 
selected specimens which I studied could be completely and 
satisfactorily accounted for by the evidence presented of under- 
feeding and parasitic infection. Moreover, a few very ill 



2 The diseases produced in sheep by Thysanosoma actinioides 
formed the subject of a paper presented by me before the Associa- 
tion of American Pathologists and Bacteriologists in April, 1912, 
in which I described a new form of biliary hepatitis due to in- 
fection with this tapeworm. 

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[235 J sheep, which were regarded by the ranchmen as typical ex- 
amples of severe loco-weed disease, were kept under observa- 
tion, and exhibited a distinct distaste for the loco-weed. At 
autopsy they were found to be emaciated, and to be infested 
with parasites. I therefore concluded that the animals which 
I had observed, although called locoed sheep by expert western 
ranchers, did not owe their condition to loco-weed poisoning, 
but were, in fact, examples of poorly nourished sheep, usually 
suffering from parasitic infection. 

During 1904, in addition to continuing the examination of 
locoed sheep, an experiment was carried out of rather an elabo- 
rate nature in an attempt to produce pure loco disease in sheep 
by feeding them upon loco-weed. A tract of public land upon 
which the loco-weed, Arag alius spicatus (Hook.) Rydberg, 
was very abundant, and where no other poisonous plant could 
be found, was fenced in and divided into several lots. Eighty 
sheep — lambs, ewes and yearlings — were selected from a 
healthy looking flock and were dosed thoroughly with thymol 
and creosote in order to rid them of parasites. They were then 
divided into several groups and placed in a series of corrals. 
The sheep in some corrals were not allowed to eat loco-weed, 
but were fed abundantly with alfalfa hay. A second group 
were given only one-half rations of alfalfa hay, but no loco- 
weed. A third group were given no alfalfa hay, but plenty of 
loco- weed. A fourth group were given one-half rations of 
alfalfa hay and plenty of loco-weed. Another group were 
given plentiful rations of alfalfa hay and were also allowed to 
feed freely on loco-weed. The experiment was continued from 
July 15 to September 6, 1904, 54 days. The details of this 
experiment are recorded elsewhere. It will suffice to sum- 
marize the results here. 

It appeared that the healthy sheep did not eat the loco-weed 
if they could. easily obtain a plentiful supply of green forage, 
but it was easy to force them to adopt a loco- weed diet by 
reducing their food, or by reducing available green forage, 
even when the animals were given a plentiful supply of cut 
alfalfa hay. When once the animal had started to eat the loco- 
weed, in no instance did they appear to eat it to the exclusion 
of other food, although they may eat rather more of loco- 

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weed than of any other single plant and may show rather a [235] 
preference for it. In no instance did an animal eating the 
loco-weed exhibit any characteristic symptoms. 

The animals which were not given alfalfa but were forced 
to feed on the loco-weed and the small amount of other forage 
in the corral suffered markedly from starvation. It was clear 
that this was no specific effect of the loco-weed because the 
animals receiving abundant alfalfa and also eating abundantly 
of loco-weed kept in much better condition and gained more 
in weight than those animals receiving only alfalfa and not 
eating loco-weed. In other words it appeared from this experi- 
ment that alfalfa and loco-weed is a better food for sheep than 
alfalfa alone and moreover it appeared that loco-weed alone 
does not keep the animal in a good state of nutrition. 

Several other interesting points were indicated by this ex- 
periment. The sheep were divided into sets, some of which 
received salt regularly and others did not receive any salt 
during the course of the experiment. Strangely enough the 
animals which received salt gained less in weight than those 
which were unsalted, and among the animals which lost weight 
the unsalted lost less weight than the salted animals. The 
young animals were more severely affected by the insufficient 
diet than the adult sheep. 

During the course of the experiment sheep fly disease 
(Myiosis), attacked all the corrals and was exceedingly severe 
in its effects upon the starved animals while the better nour- 
ished ones escaped with little damage, the sheep receiving 
alfalfa and loco-weed suffering less than any others. 

The outcome of this experiment was to convince me that 
none of the abnormalities encountered in the sheep which I 
had studied could be attributed to the poisonous action of the 
loco-weed. None of my sheep gave the slightest evidence of 
having suffered any ill results from eating the weed. On the 
other hand the experiment seemed to confirm the view 
advanced in 1903 that the animals were suffering chiefly from 
starvation combined with one type or more of parasitic 
infection. 

My conclusions are at variance with the opinion held by [236] 
members of the United States Department of Agriculture and 

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[23G] further experiments have subsequently been conducted on the 
most elaborate scale by Crawford and Marsh. Crawford's 
work which led to the conclusion that the symptoms of loco 
disease are due to barium poisoning was soon upset by a publi- 
cation by Alsberg and Black from the Department of Agri- 
culture. Marsh's work is hitherto the last word from the 
Department on the subject of loco disease. I have gone most 
carefully and painstakingly over the available reports from 
Marsh and his colleagues and find that the several reports con- 
tain perplexing contradictions, and are lacking in important 
scientific details which it is necessary for Marsh to supply 
before his conclusions can be accepted. So far as I can make 
out from a careful study, Marsh claims that he has been able 
to produce with regularity, definite and fatal forms of poison- 
ing in sheep, horses, and cattle by feeding them for a long 
time on loco-weed. Very few of his animals developed symp- 
toms of locoism until they had been feeding on loco- weed 
longer than had my experimental sheep. He claims that there 
are definite and diagnostic symptoms which can be easily 
recognized when once they have been seen, and moreover — 
which is even more important, he claims that there are diag- 
nostic anatomic changes in the animals which have died of 
loco poisoning. These anatomic changes consist essentially 
in ulceration and congestion of the stomach of horses or of the 
fourth stomach of sheep and cattle; of pronounced anemia; 
and of what are spoken of as serous collections around the 
heart and around the spinal canal outside of the dura mater. 
In the latter situation the so-called serous collections are 
frequently found in a state of organization. In addition there 
are frequently hemorrhages into the ventricles of the brain. 
In my more elaborate report I have analyzed carefully the 
writings of Marsh and have come to the conclusion that Marsh 
has by no means established the fact that the conditions he 
describes are due to loco-weed, and that up to the present time 
his work must be taken as a further substantiation of my 
claim that " loco disease " is not a clinical entity, because he 
has added one more to the list of diseases which go by the name 
of " loco-weed disease." Until Marsh gives definite and con- 
clusive reports upon the nature of these remarkable spinal 

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coagula and definitely excludes the possibilities of spinal [236] 
meningitis and meningoencephalitis, and until he fulfils other 
necessary requirements it cannot fairly be claimed that he has 
established loco-weed disease either as a clinical or as a patho- 
logic entity. 

The situation as it now stands is about this : The western 
ranchmen have for years been suffering heavy losses which 
have been attributed to the poisonous action of the loco-weed. 

The Department of Agriculture, through Marsh's publica- 
tions, has adopted the view that the ranchmen are correct in 
imputing their heavy losses to the loco-weed. Marsh urges 
the launching of a very expensive campaign against the loco- 
weed, with the object of eradicating it, a campaign for which 
I can find no reasonable justification. 

My investigations have convinced me that there are several 
diseases of western livestock masquerading under the general 
name "loco disease." One hundred per cent of the severely 
" locoed " sheep which I studied were not suffering from 
locoism, but from underfeeding combined with parasitic infec- 
tion. I therefore think there is reason to be doubtful as to the 
existence of pure, bona fide loco-weed poisoning, and I hold 
that it is perfectly certain that the heavy losses attributed to 
loco-weed disease, are at least in large measure due to other 
causes, which can usually be ascertained by careful study. 

My investigations have brought to light several dangerous 
parasitic diseases of western live stock, and I have emphasized 
the fact that it is common for the animals to be distinctly 
underfed. My conclusions have received support during the 
last ten years through several publications from the Bureau 
of Animal Industry, dealing with various parasitic diseases 
of western live stock. A study of the literature upon the 
subject, and of the works of Marsh and Crawford, and a review 
of my own work leads me to believe that the very serious losses 
which occur among western live stock raisers demand atten- 
tion, and that their interests can best be served, not by a blind 
assault upon the loco-weed, but by a vigorous campaign 
directed first at combatting the overstocking of ranches and 
the underfeeding of stock, and second at combatting the para- 
sitic diseases prevalent over the western ranges. 



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